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561.
Estimating boundary currents from satellite altimetry: A case study for the east coast of India 总被引:1,自引:0,他引:1
Fabien Durand Doraiswamy Shankar Florence Birol S. Satheesh Chandra Shenoi 《Journal of Oceanography》2008,64(6):831-845
We present a methodology to derive surface geostrophic current from a newly released altimetric sea-level data set. TOPEX/Poseidon
data were first completely reprocessed from Geophysical Data Records using new algorithms accommodating marginal seas and
coastal conditions. The methodology applied to the reprocessed data essentially consists of a smoothing of the raw along-track
coastal altimetric data at scales at which the geostrophic equilibrium holds. This was reduced to a computational procedure
using a set of objective criteria. We have applied the method to the East India Coastal Current (EICC) at the western boundary
of the Bay of Bengal. This paper first examines the quality of the new data set, which compares well with tide-gauge data;
the current we derived is consistent with independent estimates. Our methodology reveals the full spectrum of the along-shore
current, ranging from intra-seasonal to inter-annual time scales, from the deep ocean to the shelf-break area where the EICC
exists. The algorithm can be applied to any coastal region where an order of the Rossby radius can be defined, and it therefore
opens up bright prospects for mapping the variability of other boundary-current systems in the world ocean from altimetry. 相似文献
562.
Tourism industry has become an important part of Indian economy, and tourism development has been, however, concentrated to a few areas. Accumulation of tourism activities has reached the critical stage in most of the tourism centers, which pose serious threats to the natural environment. The Bhyundar Valley of Nanda Devi Biosphere Reserve (NDBR) in Uttarakhand State of the Indian Himalaya is a burning example of such problems. Land use/cover changes, deforestation and accumulation of garbage are some of the negative impacts of unregulated tourism in the valley. Unsustainable activities of tourists and villagers in the valley make such problems very severe. To deal with the ongoing problems and ensure community involvement in tourism management and environmental conservation, the Biosphere Reserve Authority introduced ecotourism in the form of Eco Development Committees (EDCs) in the Bhyundar Valley. Study reveals that many problems associated with tourism have been minimized to some extent with the help of EDCs but few are still prevailing in valley. However, the existing attempts to conserve the valley from the negative effects of tourism are inadequate and modifications are needed in the current initiatives. 相似文献
563.
Evaporation from porous rock plays an important role in weathering processes. In the case of salt weathering, the evaporation rate controls supersaturation of salt solutions within pores and the amount of precipitated aggressive salts, therefore weathering occurs mostly in places with intense evaporation. Evaporation also strongly affects frost, hydric and biogenic weathering, as these are influenced by water content and its temporal changes. Despite its importance, evaporation from porous rocks has seen little scientific focus. We present a study on evaporation from bare sandstone, one of the most common rocks affected by weathering. A new method that measures the evaporation rate from the surfaces of sandstone samples under field microclimate was developed and tested. Also, a simple calculation of 1D evaporation rate from bare sandstone surfaces based on Fick's law of diffusion is presented. The measurement was performed using sandstone cores (with a set depth of the vaporization plane) in a humid continental climate and measured on a roughly monthly interval for about 1 year. For the calculations, a laboratory-measured water-vapour diffusion coefficient of the sandstone, in-situ seasonally measured vaporization plane depth, and values of air humidity and temperature were used. The sensitivity analyses showed that the most important factor controlling the evaporation rate was the vaporization plane depth, while seasonal and spatial changes of air humidity and temperature were of lesser importance. The calculated evaporation rate reasonably follows measured values. For its simplicity and the small number of parameters required, the proposed method has the potential to improve knowledge of weathering and living conditions of endolithic and epilithic organisms. Further research should focus on factors affecting the evaporation rate (wind, hygroscopicity, hydrophobicity, etc.) to improve the accuracy of the calculations, as well as to test the applicability of the method for other lithologies and climates. © 2020 John Wiley & Sons, Ltd. 相似文献
564.
Narayan Kumar Shrestha Nabil Allataifeh Ramesh Rudra Prasad Daggupati Pradeep K. Goel Trevor Dickinson 《水文研究》2019,33(6):920-931
Agricultural zones are significant sediment sources, but it is crucial to identify critical source areas (CSAs) of sediment yield within these zones where best management practices (BMPs) can be applied to the best effect in reducing sediment delivery to receiving water bodies rather than the economically nonviable alternative of randomly or sweepingly implementing BMPs. A storm event of a specific magnitude and hyetograph profile may, at different times, generate a greater or lesser sediment yield. The widely used agricultural nonpoint source (AGNPS) model was used to identify CSAs for sediment losses in Southwestern Ontario's agriculture‐dominated 374‐ha Holtby watershed. A storm threshold approach was adopted to identify critical periods for higher sediment losses. An AGNPS model for the Holtby watershed was set up, calibrated, and validated for run‐off volume, peak flow rate, and sediment yield for several storms. The calibrated and validated model was run for storms of increasing return periods to identify threshold storm events that would generate sediment yield greater than an acceptable value for early and late spring, summer, and fall seasons. Finally, to evaluate the potential impacts of climate change, we shifted shorter duration summer storms into spring conditions and quantified the changes in sediment yield dynamics. A 6‐hr, 7.5‐year early spring storm would generate sediment losses exceeding the acceptable limit of 0.34 t ha?1 for the season. However, summer storms (2 hr, up to 100 years) tended to generate sediment yields below those of an identifiable threshold storm. If such shorter duration summer storms occurred in spring, the sediment yield would increase by more than fivefold. A 5‐year future storm would generate an equivalent effect of a 100‐year current spring event. The high sediment delivery to be expected will have significant implications regarding the future management of water quality of receiving waters. Appropriate placement of BMPs at CSAs will thus be needed to reduce such high sediment delivery to receiving waters. 相似文献
565.
Absorption against the Cosmic Microwave Background (CMB), called the anomalous absorption, is an unusual phenomenon. The transition 111–110 at 4.829 GHz of formaldehyde (H2CO) was the first one showing the anomalous absorption. The c-C3H2 is the second molecule showing anomalous absorption through its transition 220–211 at 21.590 GHz. Structure of thioformaldehyde (H2CS) is very similar to that of the H2CO. Therefore, we have investigated about the physical conditions under which the transition 111– 110 at 1.0465 GHz of H2CS would be found in anomalous absorption in cool cosmic objects. As in case of H2CO, the anomalous absorption of 111–110 of H2CS is found sensitive to the relative collisional rates and it requires that the collisional rate for the transition 111–211 must be smaller than that for the transition 110–212. 相似文献
566.
Jana Ticha Milos Tichy Michal Kocer Michaela Honkova 《Meteoritics & planetary science》2009,44(12):1889-1895
Abstract— Near‐Earth object (NEO) research plays an increasingly important role not only in solar system science but also in protecting our planetary environment as well as human society from the asteroid and comet hazard. Consequently, interest in detecting, tracking, cataloguing, and the physical characterizing of these bodies has steadily grown. The discovery rate of current NEO surveys reflects progressive improvement in a number of technical areas. An integral part of NEO discovery is astrometric follow‐up crucial for precise orbit computation and for the reasonable judging of future close encounters with the Earth, including possible impact solutions. The KLENOT Project of the Klet Observatory (South Bohemia, Czech Republic) is aimed especially at the confirmation, early follow‐up, long‐arc follow‐up, and recovery of near‐Earth objects. It ranks among the world's most prolific professional NEO follow‐up programs. The 1.06 m KLENOT telescope, put into regular operation in 2002, is the largest telescope in Europe used exclusively for observations of minor planets and comets, and full observing time is dedicated to the KLENOT team. In this paper, we present the equipment, technology, software, observing strategy, and results of the KLENOT Project obtained during its first phase from March 2002 to September 2008. The results consist of thousands of precise astrometric measurements of NEOs and also three newly discovered near‐Earth asteroids. Finally, we also discuss future plans reflecting also the role of astrometric follow‐up in connection with the modus operandi of the next generation surveys. 相似文献
567.
We show that the excellent optical and gamma-ray data available for GRB 080319B rule out the internal shock model for the prompt emission. The data instead point to a model in which the observed radiation was produced close to the deceleration radius (∼1017 cm) by a turbulent source with random Lorentz factors of ∼10 in the comoving frame. The optical radiation was produced by synchrotron emission from relativistic electrons, and the gamma-rays by inverse-Compton scattering of the synchrotron photons. The gamma-ray emission originated both in eddies and in an inter-eddy medium, whereas the optical radiation was mostly from the latter. Therefore, the gamma-ray emission was highly variable whereas the optical was much less variable. The model explains all the observed features in the prompt optical and gamma-ray data of GRB 080319B. We are unable to determine with confidence whether the energy of the explosion was carried outwards primarily by particles (kinetic energy) or magnetic fields. Consequently, we cannot tell whether the turbulent medium was located in the reverse shock (we can rule out the forward shock) or in a Poynting-dominated jet. 相似文献
568.
Widespread agricultural activity may threaten water quality in fractured bedrock aquifers having little overburden protection. A study in Canada improves the understanding of the potential impact of agriculture on water quality in bedrock aquifers, focusing on spatial and temporal variability of nitrate and bacteria. A research site was developed in and adjacent to a hay field where a gneissic aquifer is overlain by a thin veneer of unconsolidated glacial material. Ten wells were installed, hydraulically tested and completed as multilevel piezometers. Results of monthly sampling for nitrate, dissolved organic carbon, and E. coli show significant temporal and spatial variation in concentrations. Intensive 5-day sampling rounds conducted during baseflow and recharge conditions indicate that bacterial concentrations vary daily, with higher concentrations during recharge periods. The location of the impacted monitoring wells is correlated to an upgradient cattle pasture that is used periodically each summer. It is evident that periodic upgradient sources, dilution from recharge, and heterogeneous flow systems lead to varied and unpredictable contaminant concentrations. The temporal and spatial variability of contaminants in bedrock aquifers with minimal overburden must be considered for the protection of human health, as annual or even monthly groundwater monitoring may not capture unsafe concentrations. 相似文献
569.
Dynamics of transparent exopolymeric particles (TEP) and particle-associated carbohydrates in the Dona Paula bay, west coast of India 总被引:1,自引:0,他引:1
Surface seawater samples were collected over a period of 27 months at a shallow water station in Dona Paula bay from 1998–2000.
The samples were analyzed to assess the seasonal variations, inter-annual variability and the contributions of:
A distinct inter-annual variability was observed with an increase in the bacterial abundance, chlorophylla (Chl a), TEP and Sal-PCHO and their greater contribution to particulate organic carbon during May 1998–1999 than in June
1999–July 2000. Overall, there was no statistically significant correlation of TEP with phytoplankton biomass (Chl a), Sal-PCHO,
CPCHO and hydrodynamic conditions. A weak inverse correlation was observed between TEP and TBA (r = −0.397;p < 0.05) but the role of TEP as a C-source for bacteria was not evident. Both Sal-PCHO and CPCHO appeared to be two distinct
forms of carbohydrates. Unlike CPCHO, Sal-PCHO concentrations showed a positive trend with Chla and significant linear correlation with bacterial abundance (r = 0.44,p < 0.007,n = 48), indicating that Sal-PCHO as carbon source might have supported bacterioplankton abundance. The mean %TEP-C contribution
to the annual average organic carbon for 1998–2000 was 6.9% ± 5.8%, next only to phytoplankton-C (33.1 ± 22.1%) and greater
than bacterial-C (4.6% ± 4.6%) or carbohydrate-C (< 3.8%). Despite its greater contribution to the organic carbon pool, the
contribution of TEP-C to the benthic carbon demand and its fate in the study area could not be ascertained in this study. 相似文献
– | •transparent exopolymeric particles (TEP) concentration, |
– | •two forms of particle-associated carbohydrates — 1.5 M NaCl/saline extracted (Sal-PCHO) and 10 mM EDTA-extracted (CPCHO) and |
– | •total bacterial abundance (TBA) to particulate organic carbon pool. |
570.
Jetta Satyanarayana Loka Arun Kumar Reddy Monika Jain Kulshrestha R Nageswara Rao Umesh Chandra Kulshrestha 《Journal of Atmospheric Chemistry》2010,66(3):101-116
Samples of rain water were collected during monsoon season (June to September) of 2006 and 2007 at Hudegadde, a rural site
located in an ecological sensitive area of Western Ghats. The collected samples were analyzed for pH, conductivity and major
ions. At this site, rainwater pH varied from 4.20 to 7.39 with 5.65 as volume weighed mean. The observed mean was slightly
lower than the average pH reported at most of the Indian continental sites. Monthly variation showed that average pH of rain
water was the lowest during September (end of monsoon) and the highest during July (peak of monsoon). Overall, marine sources
had dominating influence at this site. However, significant influence of anthropogenic and crustal sources from local as well
as inter-continental regions was also noticed. As compared to NO3−, higher concentration of SO42− was noticed which might be due to contribution from industrial activities responsible for SO2 emission. At this site, influence of five types of airmass trajectories was noticed i.e. i) C.I.O. (Central part of Indian
Ocean)-when air masses blown from Maldives and nearby region of central Indian ocean. These airmasses had higher concentrations
of nss Ca2+ which did not show any adverse impact on the pH; ii) N.W.I.O.(North-West Indian Ocean)-when airmasses travelled from oceanic region close to north-east Africa. These airmassses had higher
concentrations of nss sulphate and nitrate and gave rise to acid rain; iii) S.W.I.O. (South -West Indian Ocean)- when airmasses
came from southern part of Indian ocean (close to Mauritius). During these airmasses, rain water samples had almost equal
ratio of nss SO42− and nss Ca2+ similar to N.W.I.O but very low NO3− ; iv) Gulf-when airmasses were observed coming from Gulf region. Although these airmasses contributed only 2% of the total
number of samples but carried high amount of nss SO42− which gave rise to acid rain. The second lowest pH was observed during these airmasses which might be due to very high nssSO42−/nssCa2+ ratios; v) N.W.I.O. + S.W.I.C. (North-West Indian Ocean+South-West Indian Continental)- when airmasses originated from north-west
Indian Ocean travelling towards south continental part of India and then arriving to the site. During these airmasses, samples
showed typical influence of urban activities having high concentrations of nss SO42− and NO3− leading to the lowest pH of rain water. 相似文献